rattle rattle thunder clatter boom boom boom...

[05crewcab]

Well, tightening one bolt didn't solve the problem. Looks like it's flywheel time.

anyone have a step by step on divorcing the trans from the engine? This is going to be a lot of fun lying on my back....

[RexDodge]

I am sure someone will post a step by step or you could search the FAQ section. Jack stands and a transmission jack are two things you'll need. It can be done with a floor jack but the transmission jacks are nice especially if you a doing this as a lone ranger. Just get it up in the air (jack stands), remove the driveline (have a rag handy to stuff into the tailshaft or you'll get a red bath) and all linkage/wiring. I usually put the transmission jack in place, remove the trans cross member and let the transmission down a bit. This will make the top bolts attaching the trans (to engine) easier to get at. Once you got it loose just wiggle it back. Don't let it down too soon or you can damage things. I've replaced the flexplate without completely dropping the trans. I just pulled it back enough to drop the flex plate out. You can use a large screw driver or a ring gear tool to turn the flex plate (to get to the bolts holding the flex plate. Be sure to torque the flex plate bolts and use some thread locker on the bolts. Have fun...

[67chevemall]

not the lifters? Sounds like you need a valve lash...

[chevytruckluver]

I am also in the flyweel opinion crowd.
If it is cracked it will not be seen untill you get the torque converter back far enough to see the mounting bolts. It will most likley be cracked between 2 or more of the mounting bolts

[Ackattack]

I had a very similar noise in my truck. Granted mine is a TBI 350 and it sounded like someone was beating on it with a hammer while going 75 up a hill. I changed out all kinds of sensors (~$500 worth) and it turned out to be a blown head gasket....right between cylinders 3 and 5. No overheating, no other signs of a blown head gasket except for the knocking sound.

DO A COMPRESSION CHECK to make sure its not this problem. I chased my tail for a month trying to figure it out.

Good luck man!

[05crewcab]

Sounds like I'll have a full saturday into pulling this thing off. great. I'm supposed to be replacing all my front end parts this spring, not dinkin around with mechanicals. ah, such is life when your hobby is 41 years old.

I will comp test the motor first just to be 100% positive it is the flexplate. (thanks for the heads up Ack)

Just out of curiousity, has anyone had the flexplate replaced at a shop? I'm guessing it's north of $500?

[05crewcab]

Finally got around to doing a compression test and the results are NOT what I wanted.


1 = 90
3 = -- Just hissing noise from somewhere...
5 = -- Just hissing noise from somewhere...
7 = 85
2 = 60
4 = 61
6 = 90
8 = 90

I did the test with a warm-ish engine (not operating temp), and throttle blocked open.

Is this telling me I have a HG leak between 3 & 5? what about lower numbers on 2 & 4?



what should my next steps be?

[Ackattack]

Originally Posted by 05crewcab

Finally got around to doing a compression test and the results are NOT what I wanted.


1 = 90
3 = -- Just hissing noise from somewhere...
5 = -- Just hissing noise from somewhere...
7 = 85
2 = 60
4 = 61
6 = 90
8 = 90

I did the test with a warm-ish engine (not operating temp), and throttle blocked open.

Is this telling me I have a HG leak between 3 & 5? what about lower numbers on 2 & 4?



what should my next steps be?

Just like mine...(mine were higher, but with a hot engine). Looks like its time to change head gaskets.

I pulled my engine to do mine, and put in a new fuel pump, timing chain, valve springs, and valve seals.

[05crewcab]

Spectacular.

are there any other tests I can do to make sure the heads are ok? how do I tell if they need to be redone?

currently the truck does not smoke at startup so I think the valve guides are fine....

[odog]

Are you losing coolant, milky oil? What do the spark plugs look like on 3 and 5? Sometimes these are signs of a blown head gasket, but then sometimes there are no signs. I guess if you are up in the air on what to check 1st (trans or head gasket) decide which is going to be easiest and quickest and do it 1st. Of course if your luck is anything like mine, it wont matter which you decide to check 1st, it will be the other one thats the problem. Good luck

[05crewcab]

Not losing coolant, and the oil is perfect. The plugs are light tan in color.(all 8 of them)

aside from 3 and 5 having no compression everything else seems to be in good working order.

[Sammy]

Common to find 350 heads with cracks. Time to look for someone you can trust in your area that does good machine work to check for cracks. A common way to drum up business at a machine shop is to drop off a set and then the shop swaps a cracked head n sells your own back to you. Still have both checked while your are at it. Good news is that your flex plate should be good.

[Boog]

You not only have 2 basically dead cylinders but 3 more with low numbers. You've got a weak engine. Head gaskets may not be all it needs. You should check the cylinders for wear while the heads are off. If you have to go down this far you may want to yank it out and rebuild it or just rings and bearings to freshen it up.

[rsavage]

Pull the valve cover off on the driver's side and see what is going on with 3 & 5's valves when it is being turned over (not running) If you have zero compression on these two cylinders I would think you have broken springs which allowed valves to contact pistons which bent stems which in turn doesn't allow valves to close to build compression. The hissing is the air being pumped out of either the carb or the exhaust manifold. I'd guess the exhaust valves simply because you haven't mentioned it backfiring through carb. Only a chevy small block would run with essentially 2 dead and 2 nearly dead cylinders. If you were getting a good seal on your compression check, I'd say you definitely have more than a head gasket problem.

[pumpkin]

I was originaly thinking flexplate, but after hearing the vidio. I hear the engine pinging. If you have no compression on side by each cylinders, the number one cause is a blown head gasket between the two. If this is a budget repair just do the head gasket and call it good.

[05crewcab]

It is going to be on a budget, thats for sure. Hopefully all this is going to cost me is $40 in gaskets...I'm 100% positive it's just head gaskets.

I have the valve covers off now and everthing looks good as far as I can tell. the rockers seemed loose to me, so I want to adjust the valves, but can't seem to find TDC... There are no marks on the balancer and I can't seem to get it right by the position of the rotor. (i thought i had it right and adjusted everything, but now it won't start)... any help there would be much appreciated.

[old Chevy guy]

The balancer just has a line on it the marks are on the timeing chain cover. The rockers might seem loose on a non running motor,thier hydrolic and pump up when its running. That wont cause 0 compresion unless you have valves that are so tight they stay open. That hissing you described sounds like the gasket is bad between 3 and 5 .

[bbadfred]

Originally Posted by hotrod100

Check for a broken flex plate. I just got done replacing one in a Suburban that was doing the exact same thing. It ended up having two small cracks around the mounting bolts and wouldn't make any noise until you got on it a bit then it would start snapping and popping. We really heard it when we were towing the boat! Unfortunately you may not be able to visually find the cracks until you pull the trans. I even used my borescope and couldn't see it. On a more positive note though, the parts are fairly cheap.

what he said!

[05crewcab]

Originally Posted by old Chevy guy

The balancer just has a line on it the marks are on the timeing chain cover. The rockers might seem loose on a non running motor,thier hydrolic and pump up when its running. That wont cause 0 compresion unless you have valves that are so tight they stay open. That hissing you described sounds like the gasket is bad between 3 and 5 .

Thanks, Found the line...it was crusted with dirt and grime. regardless, I think i am going to replace the balancer anyway while I have everthing apart. it has a slight wobble and looks old.

Bought my gasket kit and have been reading up. This is probably going to be the most difficult job I've done on the truck to date. I REALLY hope the heads are ok. If they and the cylinders look good I am going to pull the valves and inspect them and replace the springs.

Would it make sense to replace the lifters and pushrods too? do I need to replace the cam as well?

[old Chevy guy]

It all depends on what you find when you take the heads off. Ive done this job a few times with the motor in. Its not so bad as it sounds. I did two just on chevy vans and that was really a pain. At least you can climb right in there with the motor on your truck. Take your time ,yank the heads and go from there.Good luck and let us know what you find.

[05crewcab]

Pulled the heads tonight and confirmed the blown head gasket between #3 and #5...which is great...no more guessing.

I don't really know what I am looking at here... the valves are all visually fine, but some of them are whiteish in color. is that a bad sign?

Also, the #5 piston is a lighter color than the rest of them, and has 030 stamped into it. Does that mean that perhaps only that cylinder was bored out at some point?

And, the coolant ports in the head are a lot larger than the holes in the old and new gaskets...what is the reason behind this?

Check out the pics.

[68GMCCustom]

you posted all those pics while I was typing.

[Dunenutt]

Other than the blown head gasket, everything else looks good. May have had a slight manifold leak on the light colored valve cylinders.

You can mic the cylinders and see if it is just one hole thats .030 over. Just get a cheapo set of calipers from Harbor freight. They will be good enough to tell what's up.

Clean up the decks on the heads and block, and put a straight edge on them to check for warpage.

[05crewcab]

Originally Posted by Dunenutt

Other than the blown head gasket, everything else looks good. May have had a slight manifold leak on the light colored valve cylinders.

You can mic the cylinders and see if it is just one hole thats .030 over. Just get a cheapo set of calipers from Harbor freight. They will be good enough to tell what's up.

Clean up the decks on the heads and block, and put a straight edge on them to check for warpage.

ok, lots of new questions here...

slight manifold leak might be it because i thought the header bolts would be a complete PITA to get loose and they basically unscrewed with my fingers.

is there any reason they would only over bore one cylinder? seems odd to me.

what should i clean the decks with? brake cleaner and scotch brite pads? i'd like to remove some carbon while I am at it.

so, if the heads or block aren't warped once clean, should I be relatively safe in just reinstalling everything? is it really necessary to bring the heads to a machine shop if there are no visible issues?

[Vintage Windmills]

Originally Posted by 05crewcab

ok, lots of new questions here...

is it really necessary to bring the heads to a machine shop if there are no visible issues?

Depends on what your goals/budget/timeline are, if its just to get it driveable I would just bolt them back on and run. If I had the time and money and knew I wanted to keep the truck I'd rebuild everything.